Electrical conductors comprising single-wall carbon nanotubes

ABSTRACT

The present invention concerns electrical conductors comprising armchair single-wall carbon nanotubes. Such electrical conductors made by the invention are metallic, i.e., they will conduct electrical charges with a relatively low resistance. The amount of armchair single-wall carbon nanotubes in the electrical conductor can be greater than 10%, greater than 30%, greater than 50%, greater than 75%, and greater than 90%, of the single-wall carbon nanotubes in the electrical conductor.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of patent application Ser. No.09/722,950 filed Nov. 27, 2000 (pending) which is a divisional of patentapplication Ser. No. 08/687,665 filed Jul. 26, 1996 (now U.S. Pat. No.6,183,714 issued Feb. 6, 2001) which claims benefit of provisionalpatent applications Ser. No. 60/003,449 filed Sep. 8, 1995 and Ser. No.60/016,313 filed May 8, 1996.

SUMMARY OF THE INVENTION

The invention provides a method of making single-wall carbon nanotubesby condensing carbon vapor at appropriate conditions around the “liveend” of a carbon nanotube, preferably a single-wall carbon nanotube. Asingle-wall carbon nanotube with a live end is formed by vaporizingcarbon along with appropriate amounts of a Group VIII transition metalor mixtures of two or more Group VIII transition metals, maintaining thevapor at the proper annealing conditions and then collecting the sootand/or other material that condenses from the carbon/metal vapor. In oneembodiment of the invention, direct laser vaporization of a compositerod formed from a mixture of graphite and one or more Group VIIItransition metals produced single-wall carbon nanotubes when thetransition-metal/graphite vapor was briefly maintained in a heated tube.In another embodiment of the invention, the composite rod was vaporizedby utilizing two different laser pulses spaced apart in time to providea more uniform and effective vaporization of the composite rod.

The invention also provides a method of making ropes of single-wallcarbon nanotubes. These ropes comprise about 100 to 500 single-wallcarbon nanotubes all roughly parallel to each other arranged in atwo-dimensional (“2-D”) triangular lattice having a lattice constant ofabout 17 Angstroms (Å). Single-wall carbon nanotubes in a rope have adiameter of 13.8 Å±0.3 Å, or about 13.8 Å±0.2 Å, and are predominantover other possible sizes of single-wall carbon nanotubes. The inventioncomprises the methods of making single-wall carbon nanotubes and ropesof single-wall carbon nanotubes disclosed herein, as well as theproducts and compositions produced by those processes.

For example, a 1:1 atom mixture of cobalt and nickel was combined in anamount of 1 to 3% on an atom ratio with graphite (97 to 99 atom %carbon) and heated and pressed to form a composite rod. Portions of thattransition-metal/graphite composite rod were vaporized with a laserinside a tube maintained at a temperature of about 1000° to 1300° C. Aflowing stream of argon gas was passed through the tube and the pressurein the tube maintained at about 500 Torr. Material from one end of thegraphite/transition-metal composite rod was vaporized with a laser toform a vapor comprising carbon, cobalt and nickel. The soot collectedfrom that vapor produced single-wall carbon nanotubes in concentrationsmuch greater than observed before. About 50% or more of all of thecarbon in the deposits of product collected downstream of the compositerod were single-wall carbon nanotubes present either as individualnanotubes or as ropes of nanotubes. Other combinations of two or moreGroup VIII transition metals as well as any Group VIII transition metalused singularly will produce the single-wall carbon nanotubes in themethod of this invention, at concentrations of 0.1 to 10 atom %.Preferably, one or more Group VIII transition metals selected from thegroup of ruthenium, cobalt, nickel and platinum are used.

The invention also includes an embodiment where carbon nanotubes havinga live end, preferably single-wall carbon nanotubes, are caught andmaintained in the heated portion of the tube (annealing zone). Atungsten wire or mesh grid may be mounted in the tube downstream of thetarget to catch some of the carbon nanotubes formed from vaporization ofthe target comprising carbon and one or more Group VIII transitionmetals. After the carbon nanotube having a live end is caught, thecarbon vapor supplied to the five end of the carbon nanotube may besupplied by: (i) continued laser vaporization of the target comprisingcarbon and one or more Group VIII transition metals; (ii) stopping laservaporization of the target comprising carbon and one or more Group VIIItransition metals and starting laser vaporization of a targetcomprising, consisting essentially of or consisting of carbon, (ii)stopping laser vaporization altogether and introducing carbon to thelive end of the carbon nanotube from some other source. Step (iii) maybe accomplished, for example, by adding graphite particles, fullereneparticles, carbon vapor, carbon monoxide (CO), or hydrocarbons to theargon gas flowing past the live end of the carbon nanotube or by flowingCO or a hydrocarbon gas (without using an inert gas) past the live endof the carbon nanotube. In this embodiment, after the carbon nanotubeshaving at least one live end are formed, the oven temperature (annealingzone temperature) may be reduced. The temperature range may be 400° to1500° C., most preferably 500° to 700° C. Other features of theinvention will be apparent from the following Description of the SeveralViews of the Drawings and Detailed Description of the Invention.

DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram of an apparatus for practicing the invention.

FIG. 2A is a medium-magnification transmission electron microscope imageof single-wall nanotubes.

FIG. 2B is a high-magnification image of adjacent single-wall carbonnanotubes.

FIG. 2C is a high-magnification image of adjacent single-wall carbonnanotubes.

FIG. 2D is a high-magnification image of adjacent single-wall carbonnanotubes.

FIG. 2E is a high-magnification image of the cross-section of sevenadjacent single-wall carbon nanotubes.

FIG. 3 is a diagram of an apparatus for practicing the inventionutilizing two different laser pulses to vaporize the composite rodtarget.

DETAILED DESCRIPTION OF THE INVENTION

It is known that fullerene tubes are produced in some circumstancesalong with the production of fullerenes from vaporized carbon. Ebbesenet al. (Ebbesen I), “Large-Scale Synthesis Of Carbon Nanotubes,” Nature,Vol. 358, p. 220 (Jul. 16, 1992) and Ebbesen et al., (Ebbesen II),“Carbon Nanotubes,” Annual Review of Materials Science, Vol. 24, p. 235(1994). Such tubes are referred to herein as carbon nanotubes. Many ofthe carbon nanotubes examined early on had multiple walls, i.e., thecarbon nanotubes resembled concentric cylinders having a small cylinderin the middle immediately surrounded by a larger cylinder that in turnwas immediately surrounded by an even larger cylinder. Each cylinderrepresented a “wall” of the carbon nanotube. In theory, there is nolimit to the number of walls possible on a carbon nanotube, and carbonnanotubes having up to seven walls have been recognized in the priorart. Ebbesen II; Iijima et al., “Helical Microtubules Of GraphiticCarbon,” Nature, Vol. 354, p. 56 (Nov. 7, 1991).

Multi-wall carbon nanotubes have been discovered in carbon deposits oncarbon electrodes that have been used in carbon arc methods of makingfullerenes. Ebbesen I; Ebbesen II. It is also known that single-wallcarbon nanotubes can be made by adding a specific metal or a mixture ofspecific metals to the carbon in one or both of the carbon electrodesused in a carbon arc apparatus for making fullerenes. See Iijima et al.,“Single-Shell Carbon Nanotubes of 1 nm Diameter,” Nature, Vol. 363, p.603 (1993); and Bethune et al., “Cobalt Catalyzed Growth of CarbonNanotubes with Single Atomic Layer Walls,” Nature, Vol. 363, p. 605(1993). The prior art recognized a method of making single-wall carbonnanotubes using a DC arc discharge apparatus previously known to beuseful in making fullerenes described by U.S. Pat. No. 5,227,038.Single-wall carbon nanotubes were made using the DC arc dischargeapparatus by simultaneously evaporating carbon and a small percentage ofGroup VIII transition metal from the anode of the arc dischargeapparatus. See Iijima et al., “Single-Shell Carbon Nanotubes of 1 nmDiameter,” Nature, Vol. 363, p. 603 (1993); Bethune et al., “CobaltCatalyzed Growth of Carbon Nanotubes with Single Atomic Layer Walls,”Nature, Vol. 63, p. 605 (1993); Ajayan et al., “Growth MorphologiesDuring Cobalt Catalyzed Single-Shell Carbon Nanotube Synthesis,” Chem.Phys. Lett., Vol. 215, p. 509 (1993); Zhou et al., “Single-Walled CarbonNanotubes Growing Radially From YC₂ Particles,” Appl. Phys. Lett., Vol.65, p. 1593 (1994); Seraphin et al., “Single-Walled Tubes andEncapsulation of Nanocrystals Into Carbon Clusters,” Electrochem. Soc.,Vol. 142, p. 290 (1995); Saito et al., “Carbon Nanocapsules EncagingMetals and Carbides,” J. Phys. Chem. Solids, Vol. 54, p. 1849 (1993);Saito et al., “Extrusion of Single-Wall Carbon Nanotubes Via Formationof Small Particles Condensed Near an Evaporation Source,” Chem. Phys.Lett., Vol. 236, p. 419 (1995). It is also known that mixtures of suchmetals can significantly enhance the yield of single-wall carbonnanotubes in the arc discharge apparatus. See Lambert et al., “ImprovingConditions Toward Isolating Single-Shell Carbon Nanotubes,” Chem. Phys.Lett., Vol. 226, p. 364 (1994).

Single-wall carbon nanotubes of this invention are much more likely tobe free of defects than multi-wall carbon nanotubes. Defects insingle-wall carbon nanotubes are less likely than defects inmulti-walled carbon nanotubes because the latter can survive occasionaldefects, while the former have no neighboring walls to compensate fordefects by forming bridges between unsaturated carbon valances. Sincesingle-wall carbon nanotubes will have fewer defects, they are stronger,more conductive, and therefore more useful than multi-wall carbonnanotubes of similar diameter.

Carbon nanotubes, and in particular the single-wall carbon nanotubes ofthis invention, are useful for making electrical connectors in microdevices such as integrated circuits or in semiconductor chips used incomputers because of the electrical conductivity and small size of thecarbon nanotube. The carbon nanotubes are useful as antennas at opticalfrequencies, and as probes for scanning probe microscopy such as areused in scanning tunneling microscopes (STM) and atomic forcemicroscopes (AFM). The carbon nanotubes are also useful as strengtheningagents in any composite material that may be strengthened or combinedwith other forms of carbon such as graphite or carbon black The carbonnanotubes may be used in place of or in conjunction with carbon black intires for motor vehicles. The carbon nanotubes are useful in place of orin conjunction with graphite fibers in any application using graphitefibers including airplane wings and shafts for golf clubs and fishingrods. The carbon nanotubes may also be used in combination with moldablepolymers that can be formed into shapes, sheets or films, as is wellknown in the polymer art, to strengthen the shape, sheet or film and/orto make electrically conductive shapes, sheets or films. The carbonnanotubes are also useful as supports for catalysts used in industrialand chemical processes such as hydrogenation, reforming and crackingcatalysts.

Ropes of single-wall carbon nanotubes made by this invention aremetallic, i.e., they will conduct electrical charges with a relativelylow resistance. Ropes are useful in any application where an electricalconductor is needed, for example as an additive in electricallyconductive points or in polymer coatings or as the probing tip of an STMor AFM.

In defining carbon nanotubes, it is helpful to use a recognized systemof nomenclature. In this application, the carbon nanotube nomenclaturedescribed by M. S. Dresselhaus, G. Dresselhaus, and P. C. Eklund,Science of Fullerness and Carbon Nanotubes, Chap. 19, especially pp.756-760, (1996), published by Academic Press, 525 B Street, Suite 1900,San Diego, Calif. 92101-4495 or 6277 Sea Harbor Drive, Orlando, Fla.32877 (ISBN 0-12-221820-5), which is hereby incorporated by reference,will be used. The dual laser pulse feature described herein produces anabundance of (10,10) single-wall carbon nanotubes. The (10, 10) tubesare known as “armchair” tubes. All armchair tubes are metallic. Otherarmchair tubes are denoted as (n, n) where n is an integer from 1 toinfinity, preferably 1 to 1000 more preferably 5 to 500. The (10,10),single-wall carbon nanotubes have an approximate tube diameter of 13.8Å±0.3 Å or 13.8 Å±0.2 Å.

The present invention provides a method for making single-wall carbonnanotubes in which a laser beam vaporizes material from a targetcomprising, consisting essentially of, or consisting of a mixture ofcarbon and one or more Group VIII transition metals. The vapor from thetarget forms carbon nanotubes that are predominantly single-wall carbonnanotubes, and of those, the (10, 10) tube is predominant. The methodalso produces significant amounts of single-wall carbon nanotubes thatare arranged as ropes, i.e., the single-wall carbon nanotubes runparallel to each other as shown by FIGS. 2A-2E. Again, the (10, 10) tubeis the predominant tube found in each rope. The laser vaporizationmethod provides several advantages over the arc discharge method ofmaking carbon nanotubes: laser vaporization allows much greater controlover the conditions favoring growth of single-wall carbon nanotubes, thelaser vaporization method permits continuous operation, and the laservaporization method produces single-wall carbon nanotubes in higheryield and of better quality. As described herein, the laser vaporizationmethod may also be used to produce longer carbon nanotubes and longerropes.

Carbon nanotubes may have diameters ranging from about 1 nanometer (nm)for a single-wall carbon nanotube up to 3 nm, 5 nm, 10 nm, 30 nm, 60 nmor 100 nm for single-wall or multi-wall carbon nanotubes. The carbonnanotubes may range in length from 50 nm up to 1 millimeter (mm), 1centimeter (cm), 3 cm, 5 cm, or greater. The yield of single-wall carbonnanotubes in the product made by this invention is unusually high.Yields of single-wall carbon nanotubes greater than 10 wt %, greaterthan 30 wt % and greater than 50 wt % of the material vaporized arepossible with this invention.

As will be described further, the one or more Group VIII transitionmetals catalyze the growth in length of a carbon nanotube and/or theropes. The one or more Group VIII transition metals also selectivelyproduce single-wall carbon nanotubes and ropes of single-wall carbonnanotubes in high yield. The mechanism by which the growth in the carbonnanotube and/or rope is accomplished is not completely understood.However, it appears that the presence of the one or more Group VIIItransition metals on the end of the carbon nanotube facilitates theaddition of carbon from the carbon vapor to the solid structure thatforms the carbon nanotube. Applicants believe this mechanism isresponsible for the high yield and selectivity of single-wall carbonnanotubes and/or ropes in the product and will describe the inventionutilizing this mechanism as merely an explanation of the results of theinvention. Even if the mechanism is proved partially or whollyincorrect, the invention which achieves these results is still fullydescribed herein.

One aspect of the invention comprises a method of making carbonnanotubes and/or ropes of carbon nanotubes which comprises supplyingcarbon vapor to the live end of a carbon nanotube while maintaining thelive end of a carbon nanotube in an annealing zone. Carbon can bevaporized in accordance with this invention by an apparatus in which alaser beam impinges on a target comprising carbon that is maintained ina heated zone. A similar apparatus has been described in the literature,for example, in U.S. Pat. No. 5,300,203 which is incorporated herein byreference, and in Chai, et al., “Fullerenes with Metals Inside,” J.Phys. Chem., vol. 95, no. 20, p. 7564 (1991).

Carbon nanotubes having at least one live end are formed when the targetalso comprises a Group VIII transition metal or mixtures of two or moreGroup VIII transition metals. In this application, the term “live end”of a carbon nanotube refers to the end of the carbon nanotube on whichatoms of the one or more Group VIII transition metals are located. Oneor both ends of the nanotube may be a live end. A carbon nanotube havinga live end is initially produced in the laser vaporization apparatus ofthis invention by using a laser beam to vaporize material from a targetcomprising carbon and one or more Group VIII transition metals and thenintroducing the carbon/Group VIII transition metal vapor to an annealingzone. Optionally, a second laser beam is used to assist in vaporizingcarbon from the target. A carbon nanotube having a live end will form inthe annealing zone and then grow in length by the catalytic addition ofcarbon from the vapor to the live end of the carbon nanotube. Additionalcarbon vapor is then supplied to the live end of a carbon nanotube toincrease the length of the carbon nanotube.

The carbon nanotube that is formed is not always a single-wall carbonnanotube; it may be a multi-wall carbon nanotubes having two, five, tenor any greater number of walls (concentric carbon nanotubes).Preferably, though, the carbon nanotube is a single-wall carbon nanotubeand this invention provides a way of selectively producing (10, 10)single-wall carbon nanotubes in greater and sometimes far greaterabundance than multi-wall carbon nanotubes.

The annealing zone where the live end of the carbon nanotube isinitially formed should be maintained at a temperature of 500° to 1500°C., more preferably 1000° to 1400° C. and most preferably 1100 to 1300°C. In embodiments of this invention where carbon nanotubes having liveends are caught and maintained in an annealing zone and grown in lengthby further addition of carbon (without the necessity of adding furtherGroup VIII transition metal vapor), the annealing zone may be cooler,400° to 1500° C., preferably 400° to 1200° C., most preferably 500° to700° C. The pressure in the annealing zone should be maintained in therange of 50 to 2000 Torr., more preferably 100 to 800 Torr. and mostpreferably 300 to 600 Torr. The atmosphere in the annealing zone willcomprise carbon. Normally, the atmosphere in the annealing zone willalso comprise a gas that sweeps the carbon vapor through the annealingzone to a collection zone. Any gas that does not prevent the formationof carbon nanotubes will work as the sweep gas, but preferably the sweepgas is an inert gas such as helium, neon, argon, krypton, xenon, radon,or mixtures of two or more of these. Helium and Argon are mostpreferred. The use of a flowing inert gas provides the ability tocontrol temperature, and more importantly, provides the ability totransport carbon to the live end of the carbon nanotube. In someembodiments of the invention, when other materials are being vaporizedalong with carbon, for example one or more Group VIII transition metals,those compounds and vapors of those compounds will also be present inthe atmosphere of the annealing zone. If a pure metal is used, theresulting vapor will comprise the metal. If a metal oxide is used, theresulting vapor will comprise the metal and ions or molecules of oxygen.

It is important to avoid the presence of too many materials that kill orsignificantly decrease the catalytic activity of the one or more GroupVIII transition metals at the live end of the carbon nanotube. It isknown that the presence of too much water (H₂O) and/or oxygen (O₂) willkill or significantly decrease the catalytic activity of the one or moreGroup VIII transition metals. Therefore, water and oxygen are preferablyexcluded from the atmosphere in the annealing zone. Ordinarily, the useof a sweep gas having less than 5 wt %, more preferably less than 1 wt %water and oxygen will be sufficient. Most preferably the water andoxygen will be less than 0.1 wt %.

Preferably, the formation of the carbon nanotube having a live end andthe subsequent addition of carbon vapor to the carbon nanotube are allaccomplished in the same apparatus. Preferably, the apparatus comprisesa laser that is aimed at a target comprising carbon and one or moreGroup VIII transition metals, and the target and the annealing zone aremaintained at the appropriate temperature, for example by maintainingthe annealing zone in an oven. A laser beam may be aimed to impinge on atarget comprising carbon and one or more Group VIII transition metalswhere the target is mounted inside a quart tube that is in turnmaintained within a furnace maintained at the appropriate temperature.As noted above, the oven temperature is most preferably within the rangeof 1100° to 1300° C. The tube need not necessarily be a quartz tube; itmay be made from any material that can withstand the temperatures (1000°to 1500° C.). Alumina or tungsten could be used to make the tube inaddition to quartz.

Improved results are obtained where a second laser is also aimed at thetarget and both lasers are timed to deliver pulses of laser energy atseparate times. For example, the first laser may deliver a pulse intenseenough to vaporize material from the surface of the target. Typically,the pulse from the first laser will last about 10 nanoseconds (ns).After the first pulse has stopped, a pulse from a second laser hits thetarget or the carbon vapor or plasma created by the first pulse toprovide more uniform and continued vaporization of material from thesurface of the target. The second laser pulse may be the same intensityas the first pulse, or less intense, but the pulse from the second laseris typically more intense than the pulse from the first laser, andtypically delayed about 20 to 60 ns, more preferably 40 to 55 ns, afterthe end of the first pulse.

Examples of a typical specification for the first and second lasers aregiven in Examples 1 and 3 respectively. As a rough guide, the firstlaser may vary in wavelength from 11 to 0.1 micrometers, in energy from0.05 to 1 Joule and in repetition frequency from 0.01 to 1000 Hertz(Hz). The duration of the first laser pulse may vary from 10⁻¹³ to 10⁻⁶seconds (s). The second laser may vary in wavelength from 11 to 0.1micrometers, in energy from 0.05 to 1 Joule and in repetition frequencyfrom 0.01 to 1000 Hertz (Hz). The duration of the second laser pulse mayvary from 10⁻¹³ s to 10⁻⁶ s. The beginning of the second laser pulseshould be separated from end of the first laser pulse by about 10 to 100ns. If the laser supplying the second pulse is an ultraviolet (UV) laser(an Excimer laser for example), the time delay can be longer, up to 1 to10 milliseconds. But if the second pulse is from a visible or infrared(IR) laser, then the adsorption is preferably into the electrons in theplasma created by the first pulse. In this case, the optimum time delaybetween pulses is about 20 to 60 ns, more preferably 40 to 55 ns andmost preferably 40 to 50 ns. These ranges on the first and second lasersare for beams focused to a spot on the target composite rod of about 0.3to 10 mm diameter. The time delay between the first and second laserpulses is accomplished by computer control that is known in the art ofutilizing pulsed lasers. Applicants have used a CAMAC crate from LeCroyResearch Systems, 700 Chestnut Ridge Road, Chestnut Ridge, N.Y.10977-6499 along with a timing pulse generator from Kinetics SystemsCorporation, 11 Maryknoll Drive, Lockport, Ill. 60441 and a nanopulserfrom LeCroy Research Systems. Multiple first lasers and multiple secondlasers may be needed for scale up to larger targets or more powerfullasers may be used. The main feature of multiple lasers is that thefirst laser should evenly ablate material from the target surface into avapor or plasma and the second laser should deposit enough energy intothe ablated material in the vapor or plasma plume made by the firstpulse to insure that the material is vaporized into atoms or smallmolecules (less than ten carbon atoms per molecule). If the second laserpulse arrives too soon after the first pulse, the plasma created by thefirst pulse may be so dense that the second laser pulse is reflected bythe plasma. If the second laser pulse arrives too late after the firstpulse, the plasma and/or ablated material created by the first laserpulse will strike the surface of the target. But if the second laserpulse is timed to arrive just after the plasma and/or ablated materialhas been formed, as described herein, then the plasma and/or ablatedmaterial will absorb energy from the second laser pulse. Also, it shouldbe noted that the sequence of a first laser pulse followed by a secondlaser pulse will be repeated at the same repetition frequency as thefirst and second laser pulses, i.e., 0.01 to 1000 Hz.

In addition to lasers described in the Examples, other examples oflasers useful in this invention include an XeF (365 nm wavelength)laser, an XeCl (308 nm wavelength) laser, a KrF (248 nm wavelength)laser or an ArF (193 nm wavelength) laser.

Optionally but preferably a sweep gas is introduced to the tube upstreamof the target and flows past the target carrying vapor from the targetdownstream. The quartz tube should be maintained at conditions so thatthe carbon vapor and the one or more Group VIII transition metals willform carbon nanotubes at a point downstream of the carbon target butstill within the heated portion of the quartz tube. Collection of thecarbon nanotubes that form in the annealing zone may be facilitated bymaintaining a cooled collector in the internal portion of the fardownstream end of the quartz tube. For example, carbon nanotubes may becollected on a water cooled metal structure mounted in the center of thequartz tube. The carbon nanotubes will collect where the conditions areappropriate, preferably on the water cooled collector.

Any Group VIII transition metal may be used as the one or more GroupVIII transition metals in this invention. Group VIII transition metalsare iron (Fe), cobalt (Co), nickel (Ni), ruthenium (Ru), rhodium (Rh),palladium (Pd), osmium (Os), Iridium (Ir) and platinum (Pt). Preferably,the one or more Group VIII transition metals are selected from the groupconsisting of iron, cobalt, ruthenium, nickel and platinum. Mostpreferably, mixtures of cobalt and nickel or mixtures of cobalt andplatinum are used. The one or more Group VIII transition metals usefulin this invention may be used as pure metal, oxides of metals, carbidesof metals, nitrate salts of metals, or other compounds containing theGroup VIII transition metal. Preferably, the one or more Group VIIItransition metals are used as pure metals, oxides of metals, or nitratesalts of metals. The amount of the one or more Group VIII transitionmetals that should be combined with carbon to facilitate production ofcarbon nanotubes having a live end, is from 0.1 to 10 atom per cent,more preferably 0.5 to 5 atom per cent and most preferably 0.5 to 1.5atom per cent. In this application, atom per cent means the percentageof specified atoms in relation to the total number of atoms present. Forexample, a 1 atom % mixture of nickel and carbon means that of the totalnumber of atoms of nickel plus carbon, 1% are nickel (and the other 99%are carbon). When mixtures of two or more Group VIII transition metalsare used, each metal should be 1 to 99 atom % of the metal mix,preferably 10 to 90 atom % of the metal mix and most preferably 20 to 80atom % of the metal mix. When two Group VIII transition metals are used,each metal is most preferably 30 to 70 atom % of the metal mix. Whenthree Group VIII transition metals are used, each metal is mostpreferably 20 to 40 atom % of the metal mix.

The one or more Group VIII transition metals should be combined withcarbon to form a target for vaporization by a laser as described herein.The remainder of the target should be carbon and may include carbon inthe graphitic form, carbon in the fullerene form, carbon in the diamondform, or carbon in compound form such as polymers or hydrocarbons, ormixtures of two or more of these. Most preferably, the carbon used tomake the target is graphite.

Carbon is mixed with the one or more Group VIII transition metals in theratios specified and then, in the laser vaporization method, combined toform a target that comprises the carbon and the one or more Group VIIItransition metals. The target may be made by uniformly mixing carbon andthe one or more Group VIII transition metals with carbon cement at roomtemperature and then placing the mixture in a mold. The mixture in themold is then compressed and heated to about 130° C. for about 4 or 5hours while the epoxy resin of the carbon cement cures. The compressionpressure used should be sufficient to compress the mixture of graphite,one or more Group VIII transition metals and carbon cement into a moldedform that does not have voids so that the molded form will maintainstructural integrity. The molded form is then carbonized by slowlyheating it to a temperature of 810° C. for about 8 hours under anatmosphere of flowing argon. The molded and carbonized targets are thenheated to about 1200° C. under flowing argon for about 12 hours prior totheir use as a target to generate a vapor comprising carbon and the oneor more Group VIII transition metals.

The invention may be further understood by reference to FIG. 1 which isa cross-section view of laser vaporization in an oven. A target 10 ispositioned within tube 12. The target 10 will comprise carbon and maycomprise one or more Group VIII transition metals. Tube 12 is positionedin oven 14 which comprises insulation 16 and heating element zone 18.Corresponding portions of oven 14 are represented by insulation 16′ andheating element zone 18′. Tube 12 is positioned in oven 14 so thattarget 10 is within heating element zone 18.

FIG. 1 also shows water cooled collector 20 mounted inside tube 12 atthe downstream end 24 of tube 12. An inert gas such as argon or heliummay be introduced to the upstream end 22 of tube 12 so that flow is fromthe upstream end 22 of tube 12 to the downstream end 24. A laser beam 26is produced by a laser (not shown) focused on target 10. In operation,oven 14 is heated to the desired temperature, preferably 1100° to 1300°C., usually about 1200° C. Argon is introduced to the upstream end 22 asa sweep gas. The argon may optionally be preheated to a desiredtemperature, which should be about the same as the temperature of oven14. Laser beam 26 strikes target 10 vaporizing material in target 10.Vapor from target 10 is carried toward the downstream end 24 by theflowing argon stream. If the target is comprised solely of carbon, thevapor formed will be a carbon vapor. If one or more Group VIIItransition metals are included as part of the target, the vapor willcomprise carbon and one or more Group VIII transition metals.

The heat from the oven and the flowing argon maintain a certain zonewithin the inside of the tube as an annealing zone. The volume withintube 12 in the section marked 28 in FIG. 1 is the annealing zone whereincarbon vapor begins to condense and then actually condenses to formcarbon nanotubes. The water cooled collector 20 may be maintained at atemperature of 700° C. or lower, preferably 500° C. or lower on thesurface to collect carbon nanotubes that were formed in the annealingzone.

In one embodiment of the invention, carbon nanotubes having a live endcan be caught or mounted on a tungsten wire in the annealing zoneportion of tube 12. In this embodiment, it is not necessary to continueto produce a vapor having one or more Group VIII transition metals. Inthis case, target 10 may be switched to a target that comprises carbonbut not any Group VIII transition metal, and carbon will be added to thelive end of the carbon nanotube.

In another embodiment of the invention, when the target comprises one ormore Group VIII transition metals, the vapor formed by laser beam 26will comprise carbon and the one or more Group VIII transition metals.That vapor will form carbon nanotubes in the annealing zone that willthen be deposited on water cooled collector 20, preferably at tip 30 ofwater cooled collector 20. The presence of one or more Group VIIItransition metals in the vapor along with carbon in the vaporpreferentially forms carbon nanotubes instead of fullerenes, althoughsome fullerenes and graphite will usually be formed as well. In theannealing zone, carbon from the vapor is selectively added to the liveend of the carbon nanotubes due to the catalytic effect of the one ormore Group VIII transition metals present at the live end of the carbonnanotubes.

FIG. 3 shows an optional embodiment of the invention that can be used tomake longer carbon nanotubes wherein a tungsten wire 32 is stretchedacross the diameter of tube 12 downstream of target 10 but still withinthe annealing zone. After laser beam pulses hit the target 10 forming acarbon/Group VII transition metal vapor, carbon nanotubes having liveends will form in the vapor. Some of those carbon nanotubes will becaught on the tungsten wire and the live end will be aimed toward thedownstream end 24 of tube 12. Additional carbon vapor will make thecarbon nanotube grow. Carbon nanotubes as long as the annealing zone ofthe apparatus can be made in this embodiment. In this embodiment, it ispossible to switch to an all carbon target after initial formation ofthe carbon nanotubes having a live end, because the vapor need onlycontain carbon at that point.

FIG. 3 also shows part of second laser beam 34 as it impacts on target10. In practice, laser beam 26 and second laser beam 34 would be aimedat the same surface of target 10, but they would impact that surface atdifferent times as described herein.

It is also possible to stop the laser or lasers altogether. Once thesingle-wall carbon nanotube having a live end is formed, the live endwill catalyze growth of the single-wall carbon nanotube at lowertemperatures and with other carbon sources. The carbon source can beswitched to fullerenes, that can be transported to the live end by theflowing sweep gas. The carbon source can be graphite particles carriedto the live end by the sweep gas. The carbon source can be a hydrocarbonthat is carried to the live end by a sweep gas or a hydrocarbon gas ormixture of hydrocarbon gasses introduced to tube 12 to flow past thelive end. Hydrocarbons useful include methane, ethane, propane, butane,ethylene, propylene, benzene, toluene or any other paraffinic, olefinic,cyclic or aromatic hydrocarbon, or any other hydrocarbon.

The annealing zone temperature in this embodiment can be lower than theannealing zone temperatures necessary to initially form the single-wallcarbon nanotube having a live end. Annealing zone temperatures can be inthe range of 400° to 1500° C., preferably 400 to 1200° C., mostpreferably 500° to 700° C. The lower temperatures are workable becausethe Group VIII transition metal(s) catalyze the addition of carbon tothe nanotube at these lower temperatures.

The invention may also be understood by reference to the followingexamples.

EXAMPLE 1

The oven laser-vaporization apparatus described in FIG. 1 and alsodescribed by Haufler et al., “Carbon Arc Generation of C₆₀ ,” Mat. Res.Soc. Symp. Proc., Vol. 206, p. 627 (1991) and by U.S. Pat. No. 5,300,203was utilized. An Nd:YAG laser was used to produce a scanning laser beamcontrolled by a motor-driven total reflector that was focused to a 6 to7 mm diameter spot onto a metal-graphite composite target mounted in aquartz tube. The laser beam scans across the target's surface undercomputer control to maintain a smooth, uniform face on the target. Thelaser was set to deliver a 0.532 micron wavelength pulsed beam at 300milliJoules per pulse. The pulse rate was 10 hertz and the pulseduration was 10 nanoseconds (ns).

The target was supported by graphite poles in a 1-inch quartz tubeinitially evacuated to 10 m Torr. and then filled with 500 Torr. argonflowing at 50 standard cubic centimeters per second (sccm). Given thediameter of the quartz tube, this volumetric flow results in a linearflow velocity through the quartz tube in the range of 0.5 to 10 cm/sec.The quartz tube was mounted in a high-temperature furnace with a maximumtemperature setting of 1200° C. The high-temperature furnace used was aLindberg furnace 12 inches long and was maintained at approximately1000° to 1200° C. for the several experiments in Example 1. The laservaporized material from the target and that vaporized material was sweptby the flowing argon gas from the area of the target where it wasvaporized and subsequently deposited onto a water-cooled collector, madefrom copper, that was positioned downstream just outside the furnace.

Targets were uniformly mixed composite rods made by the followingthree-step procedure: (i) the paste produced from mixing high-puritymetals or metal oxides at the ratios given below with graphite powdersupplied by Carbone of America and carbon cement supplied by Dylon atroom temperature was placed in a 0.5 inch diameter cylindrical mold,(ii) the mold containing the paste was placed in a hydraulic pressequipped with heating plates, supplied by Carvey, and baked at 130° C.for 4 to 5 hours under constant pressure, and (iii) the baked rod(formed from the cylindrical mold) was then cured at 810° C. for 8 hoursunder an atmosphere of flowing argon. For each test, fresh targets wereheated at 1200° C. under flowing argon for varying lengths of time,typically 12 hours, and subsequent runs with the same targets proceededafter 2 additional hours heating at 1200° C.

The following metal concentrations were used in this example: cobalt(1.0 atom per cent), copper (0.6 atom per cent), niobium (0.6 atom percent), nickel (0.6 atom per cent), platinum (0.2 atom per cent), amixture of cobalt and nickel (0.6 atom per cent/0.6 atom per centrespectively),a mixture of cobalt and platinum (0.6 atom per cent/0.2atom per cent respectively), a mixture of cobalt and copper (0.6 atomper cent/0.5 atom per cent respectively), and a mixture of nickel andplatinum (0.6 atom per cent/0.2 atom per cent respectively). Theremainder of the mixture was primarily graphite along with small amountsof carbon cement. Each target was vaporized with a laser beam and thesoots collected from the water-cooled collector were then collectedseparately and processed by sonicating the soot for 1 hour in a solutionof methanol at room temperature and pressure (other useful solventsinclude acetone, 1,2-dicholoroethane, 1-bromo, 1,2-dichioroethane, andN,N-dimethylformamide). With one exception, the products collectedproduced a homogeneous suspension after 30 to 60 minutes of sonicationin methanol. One sample vaporized from a mixture of cobalt, nickel andgraphite was a rubbery deposit having a small portion that did not fullydisperse even after 2 hours of sonication in methanol. The soots werethen examined using a transmission electron microscope with a beamenergy of 100 keV (Model JEOL 2010).

Rods (0.5 inch diameter) having the Group VIII transition metal ormixture of two Group VIII transition metals described above wereevaluated in the experimental apparatus to determine the yield andquality of single-wall carbon nanotubes produced. No multi-wall carbonnanotubes were observed in the reaction products. Yields alwaysincreased with increasing oven temperature up to the limit of the ovenused (1200° C.). At 1200° C. oven temperature, of the single metalsutilized in the example, nickel produced the greatest yield ofsingle-wall carbon nanotubes followed by cobalt. Platinum yielded asmall number of single-wall carbon nanotubes and no single-wall carbonnanotubes were observed when carbon was combined only with copper oronly with niobium. With respect to the mixtures of two Group VIIItransition metal catalysts with graphite, the cobalt/nickel mixture andthe cobalt/platinum mixtures were both approximately equivalent and bothwere the best overall catalysts in terms of producing yields ofsingle-wall carbon nanotubes. The yield of single-wall carbon nanotubesfor both of these two metal mixtures were 10 to 100 times the yieldobserved when only one Group VIII transition metal was used. The mixtureof nickel and platinum with graphite also had a higher yield ofsingle-wall carbon nanotubes than a single metal alone. Thecobalt/copper mixture with graphite produced a small quantity ofsingle-wall carbon nanotubes.

The cobalt/nickel mixture with graphite and the cobalt/platinum mixturewith graphite both produced deposits on the water cooled collector thatresembled a sheet of rubbery material. The deposits were removed intact.The cobalt/platinum mixture produced single-wall carbon nanotubes in ayield estimated at 15 weight per cent of all of the carbon vaporizedfrom the target. The cobalt/nickel mixture produced single-wall carbonnanotubes at yields of over 50 wt % of the amount of carbon vaporized.

The images shown in FIGS. 2A through 2E are transmission electronmicrographs of single-wall carbon nanotubes produced by vaporizing atarget comprising graphite and a mixture of cobalt and nickel (0.6 atomper cent/0.6 atom per cent respectively) at an oven temperature of 1200°C. FIG. 2A shows a medium-magnification view (where the scale barrepresents 100 mm) showing that almost everywhere, bundles ofsingle-wall carbon nanotubes are tangled together with other single-wallcarbon nanotubes. FIG. 2B is a high-magnification image of one bundle ofmultiple single-wall carbon nanotubes that are all roughly parallel toeach other. The single-wall carbon nanotubes all have a diameter ofabout 1 nm, with similar spacing between adjacent single-wall carbonnanotubes. The single-wall carbon nanotubes adhere to one another by vander Waals forces.

FIG. 2C shows several overlapping bundles of single-wall carbonnanotubes, again showing the generally parallel nature of eachsingle-wall nanotube with other single-wall carbon nanotubes in the samebundle, and showing the overlapping and bending nature of the variousbundles of single-wall carbon nanotubes. FIG. 2D shows several differentbundles of single-wall carbon nanotubes, all of which are bent atvarious angles or arcs. One of the bends in the bundles is relativelysharp, illustrating the strength and flexibility of the bundle ofsingle-wall carbon nanotubes. FIG. 2E shows a cross-sectional view of abundle of 7 single-wall carbon nanotubes, each running roughly parallelto the others. All of the transmission electron micrographs in FIGS. 2Athrough 2E clearly illustrate the lack of amorphous carbon overcoatingthat is typically seen in carbon nanotubes and single-wall carbonnanotubes grown in arc-discharge methods. The images in FIGS. 2A through2E also reveal that the vast majority of the deposit comprisessingle-wall carbon nanotubes. The yield of single-wall carbon nanotubesis estimated to be about 50% of the carbon vaporized. The remaining 50%consists primarily of fullerenes, multi-layer fullerenes (fullereneonions) and/or amorphous carbon.

FIGS. 2A through 2E show transmission electron microscope images of theproducts of the cobalt/nickel catalyzed carbon nanotube material thatwas deposited on the water cooled collector in the laser vaporizationapparatus depicted in FIG. 1. Single-wall carbon nanotubes weretypically found grouped in bundles in which many tubes ran togetherroughly parallel in van der Waals contact over most of their length. Thegrouping resembled an “highway” structure in which the bundles ofsingle-wall carbon nanotubes randomly criss-crossed each other. Theimages shown in FIGS. 2A through 2E make it likely that a very highdensity of single-wall carbon nanotubes existed in the gas phase inorder to produce so many tubes aligned as shown when landing on the coldwater cooled collector. There also appeared to be very little othercarbon available to coat the single-wall carbon nanotubes prior to theirlanding on the water cooled collector in the alignment shown. Evidencethat single-wall carbon nanotubes grow in the gas phase, as opposed tofor example on the walls of the quartz tube, was provided in earlierwork on multi-walled carbon nanotubes using the same method. See Guo etal., “Self-Assembly of Tubular Fullerenes,” J. Phys. Chem., Vol. 99, p.10694 (1995) and Saito et al., “Extrusion of Single-Wall CarbonNanotubes via Formation of Small Particles Condensed Near An EvaporationSource,” Chem. Phys. Lett., Vol. 236, p. 419 (1995). The high yield ofsingle-wall carbon nanotubes in these experiments is especiallyremarkable because the soluble fullerene yield was found to be about 10weight per cent, and much of the remaining carbon in the soot productconsisted of giant fullerenes and multi-layer fullerenes.

EXAMPLE 2

In this example, a laser vaporization apparatus similar to thatdescribed by FIG. 1 was used to produce longer single-wall carbonnanotubes. The laser vaporization apparatus was modified to include atungsten wire strung across the diameter of a quartz tube mounted in anoven. The tungsten wire was placed downstream of the target so that thewire was 1 to 3 cm downstream from the downstream side of the target (13to 15 cm downstream from the surface of the target being vaporized).Argon at 500 Torr. was passed through the quartz tube at a flow rateequivalent to a linear velocity in the quartz tube of about 1 cm/sec.The oven was maintained at 1200° C. and Group VIII transition metalswere combined at 1 to 3 atom % with carbon to make the target.

The pulsed laser was operated as in Example 1 for 10 to 20 minutes.Eventually, a tear drop shaped deposit formed on the tungsten wire, withportions growing to lengths of 3 to 5 mm. The deposit resembledeyelashes growing on the tungsten wire. Examination of the depositrevealed bundles of millions of single-wall carbon nanotubes.

EXAMPLE 3

Graphite rods were prepared as described in Example 1 using graphite,graphite cement and 1.2 atom % of a mixture of 50 atom % cobalt powderand 50 atom % nickel powder. The graphite rods were pressed into shapeand then formed into targets as described in Example 1. The graphiterods were then installed as targets in an apparatus as diagramed in FIG.3, except tungsten wire 32 was not used. A quartz tube holding thegraphite rod targets was placed in an oven heated to 1200° C. Argon gaswhich had been catalytically purified to remove water vapor and oxygenwas passed through the quartz tube at a pressure of about 500 Torr and aflow rate of about 50 sccm although flow rates in the range of about 1to 500 sccm (standard cubic centimeters per minute), preferably 10 to100 sccm are also useful for a 1 inch diameter flow tube. The firstlaser was set to deliver a 0.532 micron wavelength pulsed beam at 250 mJper pulse. The pulse rate was 10 Hz and the pulse duration was 5 to 10ns. A second laser pulse struck the target 50 ns after the end of thefirst pulse. The second laser was set to deliver a 1.064 micronwavelength pulsed beam at 300 mJ per pulse. The pulse rate was 10 Hz andthe pulse duration was 5 to 10 ns. The first laser was focused to a 5 mmdiameter spot on the target and the second laser was focused to a 7 mmdiameter gaussian spot having the same center point on the target as thespot from the first laser. About 1/10th of a second after the secondlaser hit the target, the first and second lasers fired again and thisprocess was repeated until the vaporization step was stopped.

About 30 mg/hr of the raw product from the laser vaporization of thetarget surface was collected downstream. The raw product comprised a matof randomly oriented single-wall carbon nanotubes. The raw product matis made up almost entirely of carbon fibers 10-20 nm in diameter and 10to 1000 microns long.

About 2 mg of the raw product mat was sonicated in 5 ml methanol forabout 0.5 hour at room temperature. Transmission Electron Microscope(TEM) analysis of the sonicated product proved that the product wascomprised mostly of ropes of single-wall carbon nanotubes, i.e., bundlesof 10 to 1000 single-wall carbon nanotubes aligned with each other(except for occasional branching) having a reasonably constant ropediameter over the entire length of the rope. The ropes were more than100 microns long and consisting of uniform diameter single-wall carbonnanotubes. About 70 to 90 wt % of the product is in the form of ropes.The individual single-wall carbon nanotubes in the ropes all terminatewithin 100 nm of each other at the end of the rope. More than 99% of thesingle-wall carbon nanotubes appear to be continuous and free fromcarbon lattice defects over all of the length of each rope.

This invention includes the ropes of single-wall carbon nanotubesdescribed herein. particularly in the Examples. Measurements show thatthe single-wall carbon nanotubes in the ropes have a diameter of 13.8Å±0.2 Å. A (10, 10) single-wall carbon nanotube has a calculateddiameter of about 13.6 Å, and the measurements on the single-wail carbonnanotubes in the ropes proves they are predominantly the (10, 10) tube.The number of single-wall carbon nanotubes in each rope may vary fromabout 5 to 5000, preferably about 10 to 1000, or 50 to 1000, and mostpreferably about 100 to 500. The diameters of the ropes range from about20 to 200 Å, more preferably about 50 to 200 Å. The (10, 10) single-wallcarbon nanotube predominates the tubes in the ropes made by thisinvention. Ropes having greater than 10%, greater than 30%, greater than50%, greater than 75%, and even greater than 90% (10, 10) single-wallcarbon nanotubes have been produced. Ropes having greater than 50%greater than 75% and greater than 90% armchair (n, n) single-wall carbonnanotubes are also made by and are a part of this invention. Thesingle-wall carbon nanotubes in each rope are arranged to form a ropehaving a 2-D triangular lattice having a lattice constant of about 17 Å.Ropes of 0.1 up to 10, 100 or 1,000 microns in length are made by theinvention. The resistivity of a rope made in accordance with thisinvention was measured to be 0.34 to 1.0 micro ohm·meters at 27° C.,proving that the ropes are metallic.

The invention also produces a “felt” of the ropes described above. Theproduct material is collected as a tangled collection of ropes stucktogether in a mat referred to herein as a “felt.” The felt materialcollected from the inventive process has enough strength to withstandhandling, and it has been measured to be electrically conductive. Feltsof 10 mm², 100 mm², 1000 mm² or greater, are formed in the inventiveprocess.

One advantage of the single-wall carbon nanotubes produced with thelaser vaporization in an oven method is their cleanliness. Typicaldischarge arc-produced single-wall carbon nanotubes are covered with athick layer of amorphous carbon, perhaps limiting their usefulnesscompared to the clean bundles of single-wall carbon nanotubes producedby the laser vaporization method. Other advantages and features of theinvention are apparent from the disclosure. The invention may also beunderstood by reference to Guo et al., “Catalytic Growth OfSingle-Walled Nanotubes By Laser Vaporization,” Chem. Phys. Lett., Vol.243, pp. 49-54 (1995) and the provisional patent applications referencedat the beginning of this disclosure.

The advantages achieved by the dual pulsed lasers insure that the carbonand metal go through the optimum annealing conditions. The dual laserpulse process achieves this by using time to separate the ablation fromthe further and full vaporization of the ablated material. These sameoptimum conditions can be achieved by using solar energy to vaporizecarbon and metals as described in U.S. application Ser. No. 08/483,045filed Jun. 7, 1995 which is incorporated herein by reference. Combiningany of the Group VIII transition metals in place of the metals disclosedin the Ser. No. 08/483,045 application will produce the single-wallcarbon nanotubes and the ropes of this invention.

1. An electrical conductor comprising single-wall carbon nanotubes,wherein at least 10% of the single-wall carbon nanotubes in theelectrical conductor are armchair single-wall carbon nanotubes.
 2. Theelectrical conductor of claim 1, wherein at least 30% of the single-wallcarbon nanotubes in the electrical conductor are armchair single-wallcarbon nanotubes.
 3. The electrical conductor of claim 1, wherein atleast 50% of the single-wall carbon nanotubes in the electricalconductor are armchair single-wall carbon nanotubes.
 4. The electricalconductor of claim 1, wherein at least 75% of the single-wall carbonnanotubes in the electrical conductor are armchair single-wall carbonnanotubes.
 5. The electrical conductor of claim 1, wherein at least 90%of the single-wall carbon nanotubes in the electrical conductor arearmchair single-wall carbon nanotubes.
 6. The electrical conductor ofclaim 1, wherein at least 10% of the single-wall carbon nanotubes in theelectrical conductor are a same type of armchair single-wall carbonnanotubes.
 7. The electrical conductor of claim 6, wherein the same typeof armchair single-wall carbon nanotubes is (10,10) single-wall carbonnanotubes.
 8. The electrical conductor of claim 1, wherein at least 30%of the single-wall carbon nanotubes in the electrical conductor are asame type of armchair single-wall carbon nanotubes.
 9. The electricalconductor of claim 1, wherein at least 50% of the single-wall carbonnanotubes in the electrical conductor are a same type of armchairsingle-wall carbon nanotubes.
 10. The electrical conductor of claim 1,wherein at least 75% of the single-wall carbon nanotubes in theelectrical conductor are a same type of armchair single-wall carbonnanotubes.
 11. The electrical conductor of claim 1, wherein at least 90%of the single-wall carbon nanotubes in the electrical conductor are asame type of armchair single-wall carbon nanotubes.
 12. An electricalconductor comprising single-wall carbon nanotubes, wherein at least 10%of the single-wall carbon nanotubes in the electrical conductor aremetallic single-wall carbon nanotubes.
 13. The electrical conductor ofclaim 12, wherein at least 30% of the single-wall carbon nanotubes inthe electrical conductor are metallic single-wall carbon nanotubes. 14.The electrical conductor of claim 12, wherein at least 50% of thesingle-wall carbon nanotubes in the electrical conductor are metallicsingle-wall carbon nanotubes.
 15. The electrical conductor of claim 12,wherein at least 75% of the single-wall carbon nanotubes in theelectrical conductor are metallic single-wall carbon nanotubes.
 16. Theelectrical conductor of claim 12, wherein at least 90% of thesingle-wall carbon nanotubes in the electrical conductor are metallicsingle-wall carbon nanotubes.
 17. An electrical conductor comprisingsingle-wall carbon nanotubes, wherein the resistivity of the electricalconductor is at most about 1 micro ohm·meter.
 18. The electricalconductor of claim 17, wherein at least 10% of the single-wall carbonnanotubes in the electrical conductor are armchair single-wall carbonnanotubes.
 19. The electrical conductor of claim 17, wherein at least30% of the single-wall carbon nanotubes in the electrical conductor arearmchair single-wall carbon nanotubes.
 20. The electrical conductor ofclaim 17, wherein at least 50% of the single-wall carbon nanotubes inthe electrical conductor are armchair single-wall carbon nanotubes. 21.The electrical conductor of claim 17, wherein at least 75% of thesingle-wall carbon nanotubes in the electrical conductor are armchairsingle-wall carbon nanotubes.
 22. The electrical conductor of claim 17,wherein at least 90% of the single-wall carbon nanotubes in theelectrical conductor are armchair single-wall carbon nanotubes.